What is a war crime and could Putin be prosecuted over Ukraine?

US President Joe Biden has called Vladimir Putin a "war criminal" - when discussing the conflict in Ukraine.

Ukrainian President Volodymyr Zelensky and UK Prime Minister Boris Johnson have previously both accused Russia of carrying out war crimes.

What is a war crime?

It may not seem like it, but "even war has rules", as the International Committee of the Red Cross puts it.

These are contained in treaties called the Geneva Conventions and a string of other international laws and agreements.

Civilians cannot be deliberately attacked - nor can the infrastructure that is vital to their survival.

Some weapons are banned because of the indiscriminate or appalling suffering they cause - such as anti-personnel landmines and chemical or biological weapons.

The sick and wounded must be cared for - including injured soldiers, who have rights as prisoners of war.